A view of the under-river portion of the tunnel, which has an internal diameter of 44 foot (13.41 metres). The under-river section of the tunnel was completely circular and due to its immense size, the top half of the tunnel was excavated first, lined and then work began on the lower half. After the main lining and concrete roadway had been completed, the cast-iron segments above the roadway level were filled with concrete; which is the process being undertaken here.

The inscription on this image describing the task being undertaken reads: